Electrochromic devices include electrochromic materials that are known to change their optical properties, such as coloration, in response to the application of an electrical potential, thereby making the device more or less transparent or more or less reflective. Typical electrochromic (“EC”) devices include a counter electrode layer (“CE layer”), an electrochromic material layer (“EC layer”) which is deposited substantially parallel to the counter electrode layer, and an ionically conductive layer (“IC layer) separating the counter electrode layer from the electrochromic layer respectively. In addition, two transparent conductive layers (“TC layers”) respectively are substantially parallel to and in contact with the CE layer and the EC layer. The EC layer, IC layer, and CE layer can be referred to collectively as an EC stack, EC thin film stack, etc.
Materials for making the CE layer, the EC layer, the IC layer and the TC layers are known and described, for example, in US. Patent Application No. 2008/0169185, incorporated by reference herein, and desirably are substantially transparent oxides or nitrides. When an electric potential is applied across the layered structure of the electrochromic device, such as by connecting the respective TC layers to a low voltage electrical source, ions, which can include Li+ ions stored in the CE layer, flow from the CE layer, through the IC layer and to the EC layer. In addition, electrons flow from the CE layer, around an external circuit including a low voltage electrical source, to the EC layer so as to maintain charge neutrality in the CE layer and the EC layer. The transfer of ions and electrons to the EC layer causes the optical characteristics of the EC layer, and optionally the CE layer in a complementary EC device, to change, thereby changing the coloration and, thus, the transparency of the electrochromic device.
Changes in coloration of a medium, which can include one or more layers, stacks, devices, etc., can be described as changes in “transmission” of the medium. As used hereinafter, transmission refers to the permittance of the passage of electromagnetic (EM) radiation, which can include visible light, through the medium, and a “transmission level” of the medium can refer to a transmittance of the medium. Where a medium changes transmission level, the medium may change from a clear transmission state (“full transmission level”) to a transmission level where a reduced proportion of incident EM radiation passes through the medium. Such a change in transmission level may cause the coloration of the medium to change, the transparency to change, etc. For example, a medium which changes from a full transmission level to a lower transmission level may be observed to become more opaque, darker in coloration, etc.
In some cases, an EC device can switch between separate transmission levels based at least in part upon application of an electric potential across the EC device. Such application, which can include applying one or more separate voltages to one or more separate layers of the EC device, can cause one or more layers of the EC stack, including the EC layer, CE layer, etc. to change coloration, transparency, etc. In some cases, it may be desirable for different regions of an EC stack to change transmission levels differently, so that application of an electric potential across the EC stack causes separate regions of the EC stack to change from to separate ones of two or more different transmission levels.
In some cases, an electrochromic device can be located in an environment which includes moisture. For example, an electrochromic device may be exposed to an ambient environment in which the ambient environment is a mixture of ambient air and water vapor. Moisture from the ambient environment can permeate through various layers of the EC device, including the EC stack. Where an EC stack is sensitive to moisture, permeation of moisture to the EC stack can cause degraded performance of the EC stack, including a degraded ability of the EC stack to change coloration based at least in part upon applied electric potential.
The various embodiments described herein are susceptible to various modifications and alternative forms. Specific embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosure to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to.